In gynodioecious species hermaphroditic plants coexist with female plants. Toivonen and Mutikainen find that experimentally increased reproductive output leads to differential costs of reproduction in the gynodioecious Geranium sylvaticum (Geraniaceae). In hermaphrodites the costs are expressed as decreased flowering, and in females as decreased seed production; overall, female plants seem to be more sensitive to the cost of reproduction than hermaphrodites. The differential costs of reproduction may contribute to annual variation in the relative seed fitness of female plants in this gynodioecious species, and consequently they might also contribute to the maintenance of the gynodioecious breeding system.